Components in blood are routinely separated by centrifugation (i.e., red cells or white cells from plasma and platelets, platelets from plasma, cryoprecipitate from plasma, etc.
A variety of mechanical devices are utilized to attempt to sequester a specific one of these components into a specific volume without allowing the infiltration of any other components.
For instance, American Association of Blood Bank standards require substantially all of the platelets in a unit of blood should be collected into a total fluid volume of approximately 50 ml. Substantially all cryoprecipitated AHF from a unit of plasma should be collected in a volume not greater than 15 ml.
However, as all of these components are in fluid communication with each other, and all the mechanical devices in practice require the settling motion of the fluid common to all components in order to separate a specific component from the others, the subsequent currents generated by the fluid in motion necessarily starts recombining the components.
For example, consider separating platelet rich plasma which includes a minor fraction of red cells by subsequent centrifugation. One step requires expressing the platelet rich plasma into a processing bag whose initial weight is known and whose subsequent weight is determined after expressing the platelet rich plasma therein.
The plasma contained within the processing bag is centrifuged so that the platelets reside near the bottom of the processing bag upon a thin cushion of red cells leaving the lighter plasma stratified thereabove. The object is to sequester the overlying plasma away from the platelets, so that the platelets can be stored for subsequent therapeutic use. It has been determined that the platelets should be suspended in 50 ml. of plasma. Calculations heretofore have had to be performed in order to first tare out the plasma receiving bag and then continuously calculate (by weighing) as the plasma is put into the plasma bag in an amount sufficient to leave behind 50 ml. of suspended platelets within the platelet bag. This procedure is laborious from two vantage points.
From a first vantage point, the scale is influenced by the orientation of the connecting tube that communicates between the two bags. This can provide an unwanted torsion on the scale, skewing the reading. Second, transfer of the processing bag from a centrifuge station to an expressing station must be done with great care so as to not remix the stratified plasma overlying the platelets. Because the manual manipulation of this procedure requires great skill and clear calculation, efforts have been made to simplify these procedures.
The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that this reference does not teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.